The present invention relates to a highly versatile fluid-actuated valve control actuator.
More particularly, the invention relates to a fluid-actuated valve control actuator which adapts to both European and US standards.
It is known that industrial valves are usually controlled by using fluid-actuated actuators which are constituted by two mutually opposite pistons, each provided with a rack whose teeth engage a shaft arranged at right angles to the translatory motion that the pistons can perform.
The translatory motion of the pistons as a consequence of the feeding of a fluid, such as for example air or oil, causes the rotation of the shaft, which is connected to the stem of a valve to be opened or closed by the actuator.
In this manner, the actuation of the pistons allows to open or close the valve controlled by the actuator.
The ISO standard prescribes that the valve stem must engage in a square seat which is formed at the lower end of the shaft and is arranged so that its sides are respectively parallel and perpendicular to the direction of the translatory motion of the pistons.
The European standard allows (as is preferable) the option of having the seat at a 45.degree. angle with respect to the direction of motion of the pistons that engage the shaft by means of their rack.
Accordingly, due to the two different standards it is necessary to produce shafts having different configurations.
The shaft for actuating the valve stem controlled by the fluid-actuated actuator in fact has, at the opposite end for engagement with the valve stem, indicator means which allow the operator to check the actual position of the controlled valve.
For this purpose, the indicator means arranged at the upper end of the shaft, which lies furthest from the end for engagement with the valve stem, are preset differently depending on whether they must indicate the opening of a valve according to European standards or the opening of a valve according to US standards.
Of course, this fact entails an increase in production costs, since it is necessary to take into account the two types of standard in the production of the shafts and of the corresponding indicator means.
One solution to this type of drawback has been to provide the end of the shaft that engages the valve stem with an octagonal seat, so as to adapt to the two types of standard.
However, this solution is unsatisfactory from the point of view of the engagement between the seat of the shaft and the stem of the valve to be controlled, since the forces applied by the shaft to the valve stem by virtue of the actuation of the pistons of the fluid-actuated actuator can cause slippage of the shaft seat on the valve stem, accordingly preventing the appropriate actuation of said valve.